This invention is generally directed to processes for the preparation of polymers, and more specifically the present invention is directed to suspension polymerization processes for the preparation of polymers and toners thereof. In one embodiment of the present invention, the process comprises the aqueous phase suspension free radical polymerization for the formation of toner polymer resins, such as styrene butadienes, styrene methacrylates, and styrene acrylates, which process avoids the utilization of stabilizers, such as tricalcium phosphate, as compared to prior art processes as illustrated, for example, in U.S. Pat. No. 4,588,108, the disclosure of which is totally incorporated herein by reference. In one embodiment, the process of the present invention relates to the preparation of toner polymers, such as styrene butadiene copolymers, by the suspension polymerization of a monomer phase comprised of monomer or monomers, and initiator with an aqueous phase of water and an iron oxide, including magnetite. In another embodiment, the process of the present invention relates to the preparation of toner polymers, such as styrene butadiene copolymers, by the suspension polymerization of a monomer phase preferably comprised of two or more monomers and initiator with an aqueous phase of water, magnetite, and an inorganic salt like a nitrite, such as sodium or potassium nitrite. Problems solved, and/or advantages associated with the processes of the present invention include, for example, avoiding the use of a stabilizer, such as tricalcium phosphate thereby, for example, eliminating the separation of this stabilizer from the product resin polymer; washing of the polymer product can be avoided; the simplification of toner preparation in that, for example, an iron oxide, such as magnetite, including the known magnetites as illustrated in Reissue U.S. Pat. No. 33,172, the disclosure of which is totally incorporated herein by reference, is added during the process for the preparation of the polymer; and economical processes for the preparation of toner polymers. It is believed that the residual ash remaining from the suspension stabilizer tricalcium phosphate may chemically interact with the charge enhancing additives selected for the toner resulting in an undesirable rapid admix behavior degradation with aging, a disadvantage avoided with the process of the present invention. There are also provided in accordance with the present invention toner compositions comprised of resin particles obtained by the processes illustrated herein, pigment particles, and optional additives, such as waxes with hydroxyl functionality, charge enhancing components, metal salts, metal salts of fatty acids, colloidal silicas and the like. In addition, the present invention is directed to developer compositions comprised of the aforementioned toners, and carrier particles. Furthermore, in another embodiment of the present invention there are provided single component toner compositions comprised of resin particles obtained by the processes illustrated herein, magnetic components such as magnetites, and optional additives such as waxes with hydroxyl functionality. The toner and developer compositions of the present invention are useful, for example, in electrostatographic, especially xerographic, imaging and printing systems, reference for example U.S. Pat. Nos. 4,265,990; 4,298,672; and U.S. Pat. No. 4,560,635, the disclosures of which are totally incorporated herein by reference.
A toner polymer, which has been developed to exhibit properties that can satisfy the stringent standards of advanced copier and duplicators, is a copolymer of styrene and butadiene comprised of, for example, a certain ratio of styrene to butadiene (89/11) moieties, a certain minimum glass transition temperature and a carefully controlled weight average molecular weight (M.sub.w) range. Emulsion polymerization is a process that can be selected for the preparation of such polymers. However, emulsion polymerization processes have a number of disadvantages including complicated and difficult to control coagulation operations necessary to separate the solid polymer from the latex produced during the emulsion polymerization process. Further, such polymerization processes result in undesirable residual contaminants. In addition, emulsion polymerization techniques can be relatively costly due to the complex processing steps required to form and separate the polymers. The polymerization of copolymers of styrene and butadiene in, for example, an aqueous medium to form styrene-butadiene copolymer particles is known. Examples of these techniques are illustrated in U.S. Pat. Nos. 2,836,584; 4,169,828 and 4,170,699. Unfortunately, these processes can have attendant disadvantages when selected for the preparation of toner resins. For example, the process of U.S. Pat. No. 2,836,584 utilizes polyvinyl alcohol to prevent the formation of a latex, a redox type polymerization initiator or catalyst, and a long chain mercaptan to control the physical properties of the copolymer. Further, materials containing mercaptans emit hydrogen sulfide into the atmosphere and the sulfurous compounds can be absorbed by paper substrates during flash fusing due to the decomposition of the mercaptan. The odor of hydrogen sulfide in xerographic copies may render such consumer products unacceptable. The polymerization processes described in U.S. Pat. Nos. 4,169,828 and 4,170,699 appear to require the presence of a bisulfite or persulfate modifier in the presence of adjunct modifier such as amino acids or glutamic acid which can adversely affect the electrical properties of electrostatic toners prepared with these materials. The polymerization of at least one polymerizable ethylenic monomer suspended in an aqueous medium often requires the presence of other materials, such as finely divided inorganic particles and additives. For example, the process disclosed in U.S. Pat. No. 2,673,194 to Grim apparently requires the presence of an anionic surface active agent and the process disclosed in U.S. Pat. No. 2,801,921 to Hutchinson et al. is accomplished in the presence of excess alkali and finely divided magnesium hydroxide. Accordingly, there was a need for an improved and more effective aqueous polymerization process for forming a suspension of certain styrene butadiene copolymer particles which may readily be separated from the reaction medium by mere filtration. There also was a need for a polymerization process which would provide toner polymers possessing properties necessary to meet the demanding requirements of modern high speed electrostatographic imaging systems. These and other needs can be provided with the process for the preparation of styrene butadiene copolymers as illustrated in U.S. Pat. No. 4,588,108, the disclosure of which is totally incorporated herein by reference. In one embodiment of the aforementioned patent, there is provided a process for forming discrete particles of a copolymer of styrene and butadiene in which a vapor phase and an aqueous phase comprising a mixture of water, styrene monomer, butadiene monomer, a suspension stabilizing agent, and a chain propagating amount of a free radical polymerization initiator insoluble in water, soluble in the styrene monomer, soluble in the butadiene monomer and having a 1 hour half life between about 50.degree. C. and about 130.degree. C., the ratio of the styrene monomer and the butadiene monomer being between about 80:20 and about 95:5 by weight, the weight proportion of water to the combination of the styrene monomer and the butadiene monomer being between about 0.8:1 and about 2:1, the suspension stabilizing agent consisting essentially of finely divided, difficulty water soluble powder, is heated in an inert atmosphere to a temperature between about 50.degree. C. and about 130.degree. C. at a pressure between about 20 psi and about 140 psi in the absence of redox initiators and mercaptan compounds, removing butadiene monomer from the vapor phase after at least about 75 percent by weight of the butadiene monomer and styrene monomer in the aqueous phase are converted to a copolymer and prior to conversion of more than about 98 percent by weight of the butadiene monomer and styrene monomer in the aqueous phase to a copolymer, and continuing heating in an inert atmosphere at a temperature between about 50.degree. C. and about 130.degree. C. at pressure between about 20 psi and about 140 psi until the Tg value of the discrete copolymer particles formed is between about 45.degree. C. and 65.degree. C. and the weight average molecular weight of the discrete copolymer particles is between about 10,000 and about 400,000. Increased molecular weight distribution of the final copolymer may be achieved by introducing an additional mixture of styrene monomer, butadiene monomer, suspension stabilizing agent and initiator to the aqueous mixture at least once during the heating step. The additional initiator can be added in a different proportion relative to the new charge of monomer compared to the origin aqueous mixture. Optimum yields and minimum residual monomer content are achieved by heating the aqueous mixture with at least two different initiators in accordance with predetermined multistage heating procedures. Any suitable styrene monomer or polymerizable styrene derivative may be employed in the polymerization process of the aforementioned patent according to the teachings thereof. Typical polymerizable styrene derivatives disclosed include alpha-methylstyrene, vinyltoluene, ethylstyrene, monochlorostyrene, dichlorostyrene, alkoxystyrenes, such as paramethoxystyrene, and the like. Styrene is preferred because of its low cost and availability. The other monomeric reactant employed in the process of the above patent is 1,3-butadiene. Also, according to the teachings of this patent any suitable chain propagating amount of a free radical polymerization initiator insoluble in water, soluble in the styrene monomer and soluble in the butadiene monomer may be employed in the process of this invention. Typical monomer soluble free radical polymerization initiators include n-lauryl peroxide, benzoyl peroxide, acetyl peroxide, decanoyl peroxide, azo-bis-isobutyronitrile t-butyl butylperbenzoate, O,O-t-butyl-O-(ethylhexyl)monoperoxycarbonate, peroxydicarbonates 2,2-azo-bis(2,4-dimethyl-l-4-methoxyvaleronitrile), 2,2-azo-bis(2,4-dimethylvaleronitrile), and mixtures thereof. Optimum results can be achieved with peroxides, peroxycarbonates peroxybenzoates, azonitrile free radical polymerization initiators, and the like. These free radical polymerization initiators should possess a half life of about 1 hour at temperatures between about 50.degree. C. and about 130.degree. C. in order to effect adequate polymerization at reaction temperatures between about 50.degree. C. and about 130.degree. C. for reaction times of less than about 8 hours. Satisfactory results may be achieved when the reaction mixture comprises from about 0.05 percent to about 6.5 percent by weight of the free radical polymerization initiator based on a total weight of the styrene monomer and butadiene monomer. A range of about 0.05 percent to about 6 percent by weight of the free radical polymerization initiator may be preferred since it provides an acceptable rate of polymerization and leads to the synthesis of copolymers with molecular properties which enable toners containing these copolymers to melt at low temperatures. Too high a concentration may result in a low molecular weight. Reaction time can be excessive when the concentration of initiator is less than about 0.05 percent. Moreover, the suspension may become unstable and result in polymers having a high molecular weight when the initiator concentration is low.
Disadvantages associated with the process of the aforementioned '108 patent can include long reaction times, for example the reaction time from initiation to completion can be 362 minutes, which includes 45 minutes to heat the reactor to 95.degree. C. from ambient temperature, 192 minutes for the reaction to proceed at 95.degree. C., 40 minutes for the reaction temperature to be increased from 95.degree. C. to 125.degree. C., 60 minutes for the reaction to proceed at 125.degree. C. and 25 minutes for the reactor to be cooled to ambient temperature. Also, with the process of the '108 patent stabilizers such as tricalcium phosphate are selected. These and other disadvantages can be avoided or minimized with the process of the present invention wherein the use of a nontoner component stabilizer such as tricalcium phosphate can be eliminated, and there can, for example, be selected as the free radical polymerization initiator Lupersol TEAC, O,O-t-amyl-O-(2-ethyl-hexyl)monoperoxide carbonate. More specifically, with the aforementioned Lupersol, available from Lucidol Division of Pennwalt Corporation, the reaction time of the process as illustrated in the '108 patent can be reduced at least by, for example, one hour, reference copending application U.S. Ser. No. 548,328, the disclosure of which is totally incorporated herein by reference, thereby enabling, for example, the reaction to be completed in 302 minutes rather than 362 minutes in an embodiment. Also, 33 minutes can be reduced from the part of the reaction where the monomers react at 95.degree. C., and 27 minutes can be reduced from the portion of the reaction where the monomers react at 125.degree. C. in embodiments disclosed in the copending application. With the processes of the present invention, the stabilizer is replaced with a component that is normally added to the resin in the manufacturing of toner, thus the disadvantages mentioned herein can be avoided or minimized. In place of the stabilizer, there can be selected in accordance with process embodiments of the present invention inorganic oxides, such as magnetites, including magnetites available from Columbian Chemicals, and preferably Mapico Black, which oxides also function as a pigment. Advantages thereof include, for example, the elimination of acid washing of the polymer resin, and elimination of the subsequent stabilizer recovery, disposal and acid neutralization steps. Another advantage is simplified toner processing because of the addition of toner component(s) during the resin production step.
Moreover, toner and developer compositions, especially those containing charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Further, there are illustrated in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer and toner compositions with charge enhancing additives, organic sulfate and sulfonate compositions; and in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, toners with alkylpyridinium halides.
The following prior art, all U.S. patents, are mentioned: U.S. Pat. No. 4,777,230 relating to free radical polymerization of certain monomers, and wherein according to the Abstract of the Disclosure these polymers are produced by a solution polymerization with an initiating amount of tertiary alkyl hydroperoxide or its derivatives, such as monoperoxy carbonates, see column 2 for example; note column 7 wherein the initiator can be O,O-t-amyl-O-(2-ethylhexyl)monoperoxy carbonate, and in column 8 wherein the initiator can be Lupersol.RTM. TAEC, O,O-t-amyl-O-(2-ethylhexyl)monoperoxy carbonate, marketed by the Lucidol Division of Pennwalt Corporation; column 9, Lupersol.RTM. TAEC, and, for example, columns 13 and 14; U.S. Pat. No. 3,326,859 which discloses a polymerization method with peroxycarbonates, see for example column 2; U.S. Pat. No. 4,277,592, see column 3 wherein as an initiator there is selected bis(2-ethyl-hexyl)percarbonate; U.S. Pat. No. 4,526,726, see column 3 for example; U.S. Pat. No. 4,613,656, see the Abstract of the Disclosure for example; and as background interest Reissue 25,763; U.S. Pat. Nos. 2,370,588; 2,475,648 and 2,839,519.